Medical implantation procedures generally involve the delivery of a desired substance (e.g. tissue, drug, microchip, etc) to a target site in a subject. One type of tool that has found use in certain procedures is the plunger-barrel type device. The use of a plunger-barrel type device for delivery typically involves the steps of loading a barrel with a desired substance, placing the distal end of the barrel at or near the target site in a subject, and ejecting the substance from the barrel by sliding a plunger through the barrel towards the distal end at the target site. Plunger-barrel type devices have also found use in extraction procedures, where a desired substance is extracted from a target site in a subject, essentially by reversing the steps used for delivery such that the substance is loaded into the barrel from the target site.
Difficulty can arise when the substance intended for extraction or delivery is fragile and/or when the target site is blocked or partially blocked by a delicate environment. Trauma to the surrounding environment or the substance itself can occur during the procedure in the event of off-target placement or unintentional movement of the device or extended duration of device use within the subject. Further tissue insult can ensue from the additional bulk of secondary devices such as cameras or fluid jets sometimes used to aid the procedure.
Thus far, plunger-barrel type devices have fallen short on a number of levels including their precision of device mobility and placement, ability to perform multiple functions, and simplicity of use in applications where the substance itself or the environment surrounding the target is delicate, for example, implantation/extraction procedures for nervous, cardiac, vascular, bone, and joint tissue.
Perhaps one of the more sensitive applications is the delivery or extraction of target substances to or from the eye, for example, implantation of retinal tissue into the subretinal space. Unfortunately, this type of surgery is rendered extremely difficult by both a delicate surrounding environment and a fragile target substance.
The subretinal space is the area between the retinal pigment epithelium (RPE) and the photoreceptors of the retina. The transparent, layered retina processes light images projected by the cornea and lens. The photoreceptor layer in the back of the retina transforms the light into electrical impulses. Other retinal layers transfer these impulses through the optic nerve to the brain which interprets the impulses into what we perceive as sight.
Normally, the photoreceptors are in close contact with the RPE. The RPE has many functions. It provides nutrition for the photoreceptors, and also removes waste products from the photoreceptors. In many diseases, the photoreceptors and retinal pigment epithelium degenerate. Such diseases include retinitis pigmentosa, dry age-related macular degeneration, Stargardt's disease, choroideremia, rod cone dystrophy, and Sjögren's reticular dystrophy. In a normal eye, there are no blood vessels in the subretinal space. However, in some retinal diseases, blood vessels and connective tissue can grow in this space. These abnormalities in the subretinal space under the retina can damage the retina in the back of the eye and can lead to blindness. Under certain disease conditions, the photoreceptors can detach very easily from the RPE. The photoreceptors will then degenerate, resulting in vision loss or blindness, while the other layers of the retina may remain functional. After removing the abnormal blood vessels, vision may be restored by replacing the diseased RPE and/or photoreceptors which may then integrate with the functional part of the retina.
Frequent causes of blindness are dry age-related macular degeneration and retinitis pigmentosa. The macula is located in the back of the eye in the central portion of the retina and is responsible for central vision. In subjects with dry age-related macular degeneration and retinitis pigmentosa, there is initially a dysfunction of the photoreceptors and/or RPE in the macular region. This results in impairment of central and/or peripheral vision. Age related macular degeneration is a disease that has been treated with piston-barrel type devices.
Retinitis pigmentosa is a term for genetically caused photoreceptor degeneration. In these subjects, the photoreceptors must be replaced. Again, such delivery can be accomplished by piston-barrel type devices.
Surgical correction of diseases in the subretinal space between the retina and the RPE is rendered extremely difficult by the environment in which the surgery must take place. Moreover, the surgical procedure disclosed herein to implant retinal tissue into the subretinal space of the eye is complicated by the fact that fetal retinal tissue is in the nature of a transparent gelatinous mass with two non-interdigitated layers, the photoreceptors and RPE, and therefore extremely fragile.
Difficulties of implanting retinal tissue have been previously noted, as discussed in U.S. Pat. No. 5,941,250; U.S. Pat. No. 6,159,218; and U.S. Pat. No. 6,156,042, which describe delivery devices for implanting retinal tissue into the subretinal space of the eye. These devices are of the plunger-barrel type and provide a “mandrel” as the plunger and a mandrel sleeve as the barrel. A tubular nozzle is telescoped over the distal end of the mandrel sleeve and is longitudinally slidable over the mandrel and onto the mandrel sleeve to eject the loaded retinal tissue. In the loaded position, the nozzle is positioned at the far distal end of the sleeve, but biased to slide back over the sleeve by a flat spring toggle having its distal end connected to the nozzle and its proximal end connected to the handpiece. However, none of U.S. Pat. No. 5,941,250; U.S. Pat. No. 6,159,218; and U.S. Pat. No. 6,156,042 teach a device with sensitive, error-reducing delivery control, a device having a nozzle that enables precise control of placement, or a device having a multifunctional mandrel.
U.S. Pat. No. 7,468,065 to Weber et al. describes a device for delivery of ocular implants, but like other devices discussed above, this device fails to meet the needs of applications involving fragile substances to be delivered or extracted, or where the target site is blocked by a delicate environment.
What are needed in the art are high-precision devices that are capable of rapid, non-invasive, delivery and/or extraction, yet simple to use and less prone to user error.